Phase-converting system



R.. HELLMUND.

I PHASE CONVERTING SYSTEM. -v APPLICATION FILED JULY 5, \91Tv I 4 SHEETS-SHEET l.

BLE. HELLMUND- PHASE coNveRTlNG SYSTEM.

APPLICATION FILED JULY 5,1917.

1,381g308. Patented June 14, 192,1a

. 4 SHEETS-SHEET 3.

WlTNESSES: INVENTOR.

Ruda/Bi E H//mZ/nl R1 E. HELLMUND. PHASE CONVERT'VING SYSTEM.

APPLICATION FILED 1u1.' 5,1917.

1,381,303, immuun@ 14,1921.

4 SHEETS-SHEET 4.

oon-o 0611006615060 vomoooymw wnNEssEs: INVENTQR y ATTORNEY RUvdo/f E Hel/mung" UNITED STATES PATENT OFFICE.

. v RUDOLF E. HELLMUND, orsWIssvALEy PENNSYLVANIA, ASSIGNOR To WEsTING HOUSE ELECTRIC & MANUEACT'UETNG COMPANY, A CORPORATION OE PENN- sYLvANIA.

PHASE-CONVERTING SYSTEM.

To allee/wm t may concern.'

Be 1t known that I, RUDOLF E. I-IELLMUND,

a subject of the Emperor of Germany, and

a resident of Swissvale, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Phase-Converting Systems, `of which the following is a specification.V

y invention relates to phase-converting systems of the type wherein energy from a single-phase alternating-current source is transformed into polyphase currents by means of a rotary phase` converter, and it has for its main object lto provide asystem of the character designated whereby a substantial voltage balancemay be maintained in the .polyphase load circuit throughout wide load variations.

\ A further object of my invention is provide a phase-converting system wherein the' direction of phase rotation in the polyphase circuit may be reversed without disturbing the operation yof instrument transformers, limit switches and other auxiliary apparatus associated therewith.

Other objects and details of my invention will hereinafter more fully appear.

Referring to the drawing, Figure 1 isa diagrammatic view of a phase-converter system embodying a phase-balancing means inserted in two mains of the polyphase circuit, a phase converter of the asynchronous type being employed; Fig. 2 is a diagrammatic is a diagrammatic view of a phase-converterview of a system similar to Fig. 1 except that a phase-converter of the synchronous type is employed. Figs. 3 and 4 are vector diagrams illustrating the operation ofthe balancing means in the systems of Figs. 1 and 2. respectively; Fig. 5 is a diagrammatirl view of a system similar to that of Fig. 2, phase-balancing inductances being shown in all the polyphase-circuitmains; and Fig. 6

system wherein are shown both means for maintaining a substantial balance over wide ranges of load change and means whereby the' direction of phase rotation in the polyphase system may be conveniently reversed.

Phase-converter systems are well known in whicha single-phasesource of alternating current is arranged to supply a polyphase alternating-current system, certain mains of said system-being connected directly to sald Specification of Letters Patent.

electrically displaced Patented June 14,

source and an additional main of said system being connected to said source through a phase converter of the rotary type comprising `an induction machine provided with a fixed primarywinding, a rotatable secondary winding and a fixed tertiary winding y with respect to said primary winding. In tem of this character, currents iiowing through the different windings of the phase converter is to produce certain inductive and resistance drops which reduce and distort the induced or tertiary phase-converter voltage, distorting and unbalancing polyphasel system.

In my U. S. Patents Nos. 1,242,936 and 1,242,937, issued Oct. 16, 1917, and assigned to the Westinghouse Electric & Manufacturing Company, I have disclosedy and claimed means whereby the balance in the polyphase system may be much improved by the insertion of inductive reactance devices in the leads which are directly connected to the single-phase source and by providing certain mutual relations between said inductive devices.

In the systems described in the aforementioned applications, the reactanoe's of the inductive devices in the different mains of the system were equal. I find that superior results may be obtained by employing reactive devices of unequal inductance in the different mains, said distributed in diiierent ways, as will hereinafter be more fully pointed out.

Referring to F 1 of the drawing, I show a source of alternating current, such, for example, as a transformer winding at 10. A polyphase load device, such, for example, as an induction motor, is shown at11 and is arranged to be energized from the single'- phase source 10 bythe aid of a phase-converter dynamo-electric machine 12 comprising a primary winding 13, a secondary winding 14 and a tertiary winding 15. The' primary winding 13 is connected directly across a. portion of the source 10.v The secondary winding 14 is shown in the form of a squirrel-,cage winding, mounted for rotation in electrical proximity to the winding 13, and the tertiary winding 15 is a stator winding also mounted in electrical proximity to the 1921. Application led July 5, 1917. Serial No. 1718,549.

thel operation of a systhe action of the load devices being arranged and the electromotive forces in the secondary winding 14 and in electrical quadrature to the primary winding 13. By so adjusting the relative number of turns in the different windings that the voltage induced in the tertiary winding 15 shall be substantially 87% of that impressed upon the primary winding 13, a three-phase electromotive force may be impressed upon the motor 11 in accordance with the Scotty or T connection, as is well known in the art, two terminals of the motor 11 being connected directly to the terminals of the source 10 through mains 16 and 17 and the remaining terminal 11 being connected to substantially the mid-point of the source 10 through the tertiary winding 15.

With the circuit arrangement thus described, a substantially balanced three-phase electromotive torce may be produced for application to the motor 11, under no-load conditions, the magnetizing current ot the converter producing small drops but, as soon as load is imposed upon the motor 11, the cumulative effect of the resistance and y' reactive drops through the converter 12 is to reduce the magnitude and shift the phase of the electromotive force provided by the winding 15, thus unbalancing the electromotive forces at the motor 11. ln order to compensate for this effect and to maintain substantial voltage balance at the load, throughout variations in the load current, I provide an inductive reactor 18 in the main 16 and a similar, though larger, inductive reactor in the main 17. The effect of the reactors 18 and 19 is to produce alternations in the magnitude and phase of the electromotive Aforces impressed upon. the motor 11 so as to maintain balance thereat, as will be understood by reference to the vector diagram of Fig. 3.

Referringl to this diagram, the electromotive force provided by the source 10 and impressed upon the primary winding 13 and also upon one phase of the load is represented by a vector 20-21, and the electromotive force produced in the tertiary winding 15 is represented, in phase and magnitude, by a vector 22%, the length of the vector 29d- 23 preferably being somewhat more than 87% of the length of the vector 20--21- Thus, the triangle 20-21-23 represents approximately the polyphase electromotive force impressed upon the motor.

In accordance with the principles of the well known Heyland diagram l'or the induction motor, the load currents for one phase of the motor 11 may be represented by vectors radiating from a central Joint 24 and having their terminals lying upon a semicircle 25--26- 27-28. The vector 2li- 25 represents, in phase and in magnitude, the loadcurrent of one phase of the motor 11 under 100% overload motoring, the vector 24e- 26 Vfor full-load motoring, the vector 'Q4-35 and 24F-36, respectively. For 100% overload-current motoring, the cumulative reactive drops through the phase converter may be indicated by a vector 23-37, perpendicular to the vector 2d- 25 and the cumulative resistance drop by a vector 237-38, parallel to the vector Qet-Ql Thus,

at 100% overload motoring, the apex of the Y polyphase voltage triangle moves to the point 38 and would result in serious unbalancing of the electromotive forces on the motor 11 were it not for the effects of the inductive devices 18 and 19. motoring, the apex of the voltage triangle assumes a position 39, for no-load, a position 10, and a full-load recuperation position L11.

At 100% overload motoring, the effect of the relatively large reactor 19 is to produce a reactive drop represented by a vector ill-112, perpendicular to the vector QMQE), thus shifting the rlocation of the point 21 to the point 412. The effect of the reactor 19, at other conditions of load, is to producedrops represented by the vectors 21-13, S21- 44 and S21-45, respectively, so that the point 21 assumes the position 18 at full-load motoring, the position 44; at no-load and the position at full-load recuperation.

In like manner, the effect of the small reactor 18 is to produce a reactive drop represented by a vector 20-4L6, at 100% overload motoring, said vector being perpendicular to the current vector 241-38 and causing the point 20 to move to the position 4:6. In like manner, the point 20 assumes the position 17 at full-load motoring, the position L18 at no-load and the position 49 at Jfull-load recuperation.

Turning now toa discussion of the general principles underlying the problem of maintaining a desirable voltage balance, it is obvious that, by inserting resistance and inductive reactance in each of the mains 16 and 17, corresponding to the resistance and inductive reactance of the phase converter 12, the drops 2338, 23-39, 23-40 and 23-41 could be duplicated for the other two vcrtices of the main three-phase-voltage triangle and the points 21 and 20 caused to be displaced by an amount similar to 4that indicated for the point 23. In this Way, the voltage balance would be maintained, although at the expense of an unnecessary reduction in the output voltage and also of marked energy loss in the ohmic resistance thus introduced. By the use of unequal reactances in the outside supply mains, as in- For full-load v;

` F ig. 3 may be considered as tending to pivot'V about the point 20 while changing in magnitude, the apex moving through a majordisl tance andthe' point 21 moving through an intermediate distance. VVlhile it is true that there is* no strict pivoting about the point 20, inthat said point does move somewhat,

it is nevertheless true that the motionfthe're- .F

of is less thanthat of the point 21, themetioncof which isless. than that ofl the apex 23. By the appropriate choice ofthe amount of reactance inthe devices 18 and 19` and: of the voltage induced yinthe tertiary winding. 15 in excess of 87% of theprimary winding of the phase converter, the triangles 38-7- 42.4c, 39413-47, 40-44-4sand 4145+ 49 may all be caused to be sornearly equilateral as to come within the commercial requirements of voltage balance.

The phase-converter 12 in. the system, of Fig. 1 is of the asynchronous type. It has also been proposed to employ phase converters of the synchronous type so that the power factor of the entire system may be controlled and improved by over-excitationof the synchronous phase converter, as is well knownand understood. A system of this type is shown in Fig. 2, it being the same asthat shown in Fig.' lexcept thatan additional winding 50 is placed upon the rotor of the phase converter12 and -is ar ranged tobe excited from a source of direct current 51. For a vector treatment of the resultant Icontrol of the polyphase voltage balance over a wide range of load change,

- attention is directed to Fig. 4 wherein the main vectors are as indicated inFig. 3. The effect of the over-'excitation offthe secondary member of the phase converter is to'produce leading wattless-current which may be rep-A resented, in phase and magnitude, by a vector 24-52. The watt or lenergy currents produce drops in all the phase-converting windings. The leading wattless'currentrep resented by the vector 24452 producesdnops principally in the primary winding 13 and partially in the secondary windings of the converter 12,whereas thel'agging wattless components of the motor currents represented by the vectors 24-.-25; 24-26, 24--27 and 24--28 producefdrops principally inthe tertiary winding 15, although also partially in the secondary windings of the phase'converter. Thus, the' equivalent currents supplied from the phase converter for the differentv conditions of load may be represented by vectors 24k- 53, -24-54, 24-55 and 21k-56, respectively. The construction of the vector 24-53 in accordance with the above'v is obvious, its wattless current component beingthe' algebraicx sum of one-half the vector' 24-52 and the wattless component" of the vector 24-25 and lits energy componentV being thev same as that .of the vector Y The ohmic andy reactive drops in the phase-converter are plotted from the'. vertex 23`,= as in F 3, with-the exception that they are taken perpendicular or parallel' to `the current vectors 24-53 to 24-56, inclusive, respectively, rather than lie reactive drops 21-421150 21-45, inelusive, and 20-#46 tof 20549, inclusive, are as in' Fig. 3.7. By choosing the vertex '23 somewhat belowand to they left of the apex of anequ'ilateraltriangle constructed on the base 20.- 2'1, that is, by'inducing an electromotivey force in theL tertiary winding 15 somewhat less'than 87% ofthe' voltage im;-f pressed uponlthe primary winding 13 'and by connecting the; tenninalof the winding 15v slightly off'the centerof'the source 10, a more desirablev voltage balanceV is main; tained', y Y y I y It k'may frequently be kundesirable to induce less than ,87% of the primaryvoltage in the tertiary' winding 15 and to connect the,v tertiary winding 15 off the center of the prima ,winding 10 and, under these conditions, mayv produce the effect osaid un-y Vsymmetrical connection by placing a small inductivedevice in thelead connected to the tertiary winding.` f Thus, in the system of Fig. 5,' an ,inductive reactor 57 is connected inseries with the tertiary winding 15. The vector diagram, under these conditions, is substantially the same as that shown in Fig. 4, the effect of the reactor 57 tending to locate the vertex of the equilateral triangle at the point 23, as is' desired. n

In the systems-described to this point, the inductive reactor located to affect the load phase immediately Aleading the electromotive force ofvthe single-phase source has been greaterthan thatlocated toafiect thejload phase immediately following the electrothe vectorst24-25' to 24e-28, inclusive, as in motive force. of the vsingle-phase supply.

principallyto correct the unbalancing caused bythe reactive drops, the unbalancing caused by the resistance drops being more diicult to control by the use of reactors in the supe before.

ply.- leads. It is generally moreconvenient to compensate -forthe resistance drops under varying degrees of load by the adjustment of the taps .supplying the phase converter.

s A vvsystem operating in accordance with both of the above .principles is indicatedin Fig. 6.v A source of single-phase current 10 is arranged to supply a polyphase induction motor 11 through a phase converter 12, as One point of attachment of the primary vwinding 13 to the supply winding 10 is adjustable, as shown'at 60, and said point lof attachment may be varied automatically by the operation ,of an induction motor 61 operated by voltage unbalance in the. system kas follows. An induction machine 62. is` provided having a secondary winding 63 connected to energize the primary winding of the motor 61'. The primary winding 64 of the motor 62 is connected to be energized by vcurrent transformers 65-66-67 arranged in the respective polyphase supply'leads. The induction machine 62 is running light and, therefore, when the currents in the different supply leads of the motor 11 are in balance, "the currents circulating in the secondary winding 63 are very small,` being insufficient to operate the motor` 61. Upon an unbalancing of the current in the supply mains of the main motor 11, the currents supplied to the primary winding 64 are unbalanced and the secondary winding 63 tends to produce a balance thereof in accordance with the well known balancing action of a polyphase induction machine. As a result, ,circulating currents flow through the primarywinding of the motor 61 sufiicient to cause ,the operation thereof and the adjustment ofthe point 60. vBy `suitable design, of the apparatus, the point 60 may be correctly adjusted, either tothe right or to the left, for'appropriate correction of the unbalancing.

Turning now to the reversal of phase rotation and the attendant reversal of the motor 11, a reversing switch 68 is provided for interchanging the terminals of the tertiary windings 15. Thus, the direction of phase rotation in the polyphase system is reversed v without affecting the phase converter itself.

A like result may be attained by reversing the connections of the primary winding of the phase-converter. Furthermore, by lo-` cating the current transformer 66 between the reversing switch 68 and 'the L*tertiary winding 15, the reversal of the phase rotation does not aEect the operation of the automatic adjusting device 62-61. In like manner, limit switches or other pieces of `control apparatus, which should be undisturbed iny operation by a reversal in phase rotation, may be located vsimilarly to the current transformer 66.

The inductive reactors 18 and 19 may have adjustable movable core members which are connected together, as by a link 69. As shown, with the reversing switch 68 thrown to the left, the link 69 is also thrown to the left so that the'entire core member of the reactory 18 is active, whereas, a portion of the core member of the reactor 19 is withdrawn from the solenoid and is, accordingly, inactive. Thus, for the particular direction of phase rotation indicated by the position of the switch 68, the reactance of the device'18 preponderates over that of the device 19.

Upon throwing the reversing switch 68 to the right, for the reversal of the phase rotation, the link 69 should also be thrown to the right, introducing the core member of they device 19. and withdrawing the core member ofthe device 18, thus causing the inductive reactance of the device 19 to preponderate over that ofthe device 18. This reactance controlling device is merely illustrative of many possible structures capable of producing the same result and I do not desire to be restricted to the specific structure shown.

' With all of the foregoing systems, the voltage balance `in the polyphase system will be somewhat better than that indicated in the vector diagrams, by reason of the inher ent balancing action ofthe polyphase induction motor 1,1. A p

While I have shownV my invention in a plurality of preferred forms it will be obviousto those skilled in the art that it is not so limited but is susceptible of various minor changes and modifications vwithoutl departing` from the spirit thereof and I desire, therefore, that only lsuch limitations vshall be placed thereupon as are imposed by the prior art or are specifically set forth in the appended claims. 4

Irclaim as my invention:`

1. The combination with a three-phase system and a single-phase system, of a dynamo-clectric phase converter for effecting an 'energy interchange between said systems, one phase of said three-phase system being directly coupled to said single-phase system, the other phases of said three-phase system being derived from said single-'phase system through said phase converter, and means for producing independent reactive drops in said last-mentionedphases of said three-phase system.

2. The method of improving the balance of the output electromotive' forces of a phase-converter system wherein three-phase currents are derived from` a singlephase source by a rotary phase-converter, one phase being derived directly from said source and being in phase therewith, which comprises producing unequal reactive drops converter having its inducing winding con- .Y

nected thereto, a polyphase load circuit having certain of its mains connected directly to said source and having another main connected to be energized from the induced winding of said converter and inductive devices of unequal reactance in kvtwoof said directly connected load-circuit mains.

4. The combination with a phase-converter system comprising a source of singlephase electromotive force, of a rotary` phase converter having its inducing winding conn nected thereto, a polyphase load circuit having certain of its mains connected directly to said source and having another main connected to be energized from` the induced,Y

winding of said converter, and inductive devicesof unequal reactance in two of said directly connected load-circuit mains, the re-` actance of the inductive device inthe phase immediately having its primary winding connectedv across said source and having its tertiary winding connected between an intermediate point in said source and a third load main, means for automatically adjusting the point of attachment of said tertiary winding to said source in accordance with the load current, and means for developing unequal inductive reactances in the phases of lsaid load circuit which are out of phasewith said source, Vthe reactance in the phase immediately leading said source in phase exceeding that in the phase immediately following said source in phase, whereby substantial load balance may be maintained in said load circuit under varying load.

6. The combination with a phase-converter system embodying a single-phase source, a three-phase load circuit, a rotary phase-converter, two mains of said load circuit being connected directly to said source unequal inductances inserted in the mains connected directly to vsaid source, of means for reversing the direction of phase rotation leading said source in phaseV exceeding that in the `phasey immediately in said load circuit, and means for reversing the inequality of said inductances.

7. The combination with a phase-converter comprising a primary stator winding, a rotatable secondary winding, and a tertiary stator winding electrically displaced from said primary winding, of a source of alternating current, a polyphase load circuit, connections from the terminals of said sourceto certain of the mains of said load circuit, connections for inserting said tertiary Vwinding between an intermediate point in said source and a main of said load circuit, means for reversing said tertiary winding in' said last-named connections, whereby the direction of phase rotation in said load circuit may be reversed, inductive devices of unequal reactance in` the two mains directly connected to said source, and means for reversing the inequality of said devices.

8. Means tending to maintain the balance of a phase-converter system embodying a single-phase alternating-current source, a

polyphase load circuit, and a rotary-phase converter, said phase-converter embodying a primary winding connected acrossV said source and a tertiary winding connected between an intermediate point in said source and a main of said load circuit, comprising an auxiliary polypliase induction machine, having primary and secondary windings and -having its primary winding connectedto be energized in' accordance with the 'currentsl in said polyphase load circuit, an electromotor device arranged to adjustfthe point of attachment of said ter tiary winding to said source, and means rfor 'energizing said device, in accordance with the currentsiiowing in the secondary winding of saidL auxiliary induction machine.

9. The combination with a Y source of single-phase alternating current, of a phaseaffected by a reversal of the v'direction of phase rotation in said polyphase circuit connected between said tertiary winding and Ysaid terminal interchanging means.

' In testimony whereof, I have hereunto subscribed myname this 28th day of June,

RUDOLF E. HELLMUND.

phase oi the electromotive force v 

